Method of conditioning photoconductor surfaces



1968 K. A. METCALFE ETAL 3,406,061

METHOD OF CONDITIONING PHOTOCONDUCTOR SURFACES Filed Dec. 8, 1964 step 1f5 J IEJQJ AB 9 3 Step4 lol $153,125

. Step 1 W IL United States Patent 3,406,061 METHOD OF CONDITIONINGPHOTO- CONDUCTOR SURFACES Kenneth A. Metealfe, Fulham Park, SouthAustralia, and

Alwin S. Clements, Largs Bay, South Australia, Australia, assignors toThe Commonwealth of Australia, The Secretary, Department of Supply,Melbourne, Victoria, Australia Filed Dec. 8, 1964, Ser. No. 416,698Claims priority, application Australia, Dec. 13, 1963, 38,833/ 63 10Claims. (Cl. 96-1) ABSTRACT OF THE DISCLOSURE A method of conditioningphotoconductor surfaces in which the image is developed in one liquidmedium and a second liquid medium is then applied which is notcompatible with the first medium so that both liquids wet differentparts of the image and then applying a decomposing agent selective toone of the liquids to decompose the photoconductor in contact with theliquid.

Drawing FIG. 1(a)-1(b) show the four sequential steps of a methodprovided in accordance with one embodiment o the invention; and

FIGS. 2(a)-(e) show the five steps of a method provided in accordancewith a second embodiment of the invention.

This invention relates to a method of conditioning photoconductorsurfaces.

Photoconductor surfaces for the production of xerographic images usuallycomprise a photoconductor which is evaporated or otherwise coated on toa surface or alternatively a particulate photoconductor is embedded inaninsulating film-forming matrix, the photoconductor in each case beingcapable of receiving a charge which can then be modified by a lightimage or the like and the electrostatic image so produced developed bycontacting the surface with developer particles having the correctcharge.

'Photoconductor surfaces of this type have been used for very manypurposes such as for the production of visible images, for the formationof printing blocks, or for the manufacture of printed circuits, thevarious processes utilizing the photoconductor surface in different waysto attain the particular objective.

It is already well known to produce an image on a photoconductor and tothen develop the image with a resist developer capable of preventingattack of the photoconductor in the areas beneath the resist so that theremainder of the photoconductor could be removed by dissolving oretching same away.

The present invention relates generally to this type type of process buthas a very much wider application and can be used wherever it isdesirable to remove a photoconductor film to give access to the surfacebeneath for etching or for any other purpose.

The method of conditioning photoconductor surfaces according to ourinvention consists in producing an electrostatic latent image on aphotoconductor surface, then developing the electrostatic latent imagewith a first liquid developer at least part of which has an aflinity forthe charged areas of the latent electrostatic image to be drawn and heldthereto, then while the first liquid devel oper remains on thephotoconductor surface wetting the surface with a second liquid which isnot compatible with the first liquid, decomposing the photoconductor bycontact with a decomposing agent which is selective to one Patented Oct.15, 1968 of the said liquids to be accepted thereby, and then removingthe photoconductor where so decomposed,

According to one method, the second liquid, which is not compatible withthe first liquid developer, contains a decomposing agent for thephotoconductor so that on application of this liquid the photoconductoris decomposed where contacted by the liquid.

Accord-ing to another method, the decomposing liquid is applied to thesurface after application of the second liquid, which decomposing liquidis chosen to be selective to one of the liquids only to combine withthat liquid and to decompose the photoconductor where contacted by thisdecomposing liquid.

By the above method when using a pure liquid developer, developmentapparently takes place through differential charging of the first liquidin relation to the electrostatic image so that the liquid is attractedto the charged image areas, and therefore if while retaining the firstliquid in place, the surface is contacted with a second liquid which isimmiscible with the first liquid, the second liquid will be deposited onthose areas which do not contain any of the first liquid, and thereforeif the second liquid is of the decomposing type, or carries adecomposing medium, or has a decomposing medium subsequently applied toone of the liquids which is compatible with that liquid, thephotoconductor surface on which it exists will be modified so that itcan be readily removed.

The method of protecting the first liquid against remo'val during thesubsequent application of the second liquid is to carry out the twoprocesses with sufficient rapidity to prevent the first liquid fromleaving the area concerned and of course under such conditions that theelectrostatic image is not destroyed. This can be achieved, for example,by making the first liquid an insulator and having the electrostaticfield hold the first liquid in place.

To facilitate the locating of the first liquid after it has beendeposited, this liquid may be of a type having a high viscosity, such asa silicone, which will then tend to remain in position, or alternativelya developer medium can be carried down with the liquid to beco-deposited therewith and thereby to ensure that the liquid is held inplace, the developer material for this purpose preferably being suchthat it can absorb the liquid to ensure better holding of same.

After deposition of the second liquid and the decomposing medium, thesurface on Which it is then acting can be wiped away or washed away inany desired manner, and it will be found that if this invention is usedsuch photoconductors as selenium or zinc oxide can be readily removed byutilizing a 5 to 10 percent solution of potassium hydroxide, sodiumsulphide or sodium hydroxide in ethyl alcohol or methyl alcohol ordiacetone or other higher alcohol.

It has been found that any substances of the character of thosementioned can be advantageously used for this invention without beinglimited to the substances mentioned.

According to a preferred method of carrying out the invention forinstance a Zinc oxide or selenium coating on paper or metal is producedin the already well known manner and this is charged and exposed to animage so that an electrostatic latent image is formed on the surface.

This image is then developed by means of a liquid developer comprisingeither a viscous high boiling point developer liquid having anelectrical resistivity in excess of 10 ohm centimetre and a dielectricconstant less than 3 which may carry a particulate material such as aresin or the like or a resin or other bonding medium in conjunction witha pigment particle, the resin or the like preferably being so selectedthat it absorbs some of the insulating liquid to hold it during thesubsequent process.

After developing the image in this way and while the image is still wetthe surface is subjected to a mixture comprising a polar substance suchas an alcohol and an insulating liquid which can be the same liquid usedfor the first part of the process, but these two liquids must not bemiscible so that the polar liquid will then be repelled by theinsulating liquid held on the image and will only be able to act to wetthe remaining surface.

A caustic medium can be placed into the alcohol so that thephotoconductor surface is decomposed where the caustic acts on it, or anadditional processing can be carried out by subjecting the surface to acaustic mixture dissolved in alcohol or other polar liquid, after firsttreating the surface with the mixture of polar and non-polar liquid.

The decomposed surface can then be readily removed by means of amechanical action such as the use of a jet of water or an abrasive, itbeing found that the effect of the decomposing of the surface being torender is read ily removable.

In the case of selenium this avoids the necessity of using carbonbisulphide as the solvent medium and therefore a much safer and betterprocess results.

For the invention to be fully appreciated various meth ods of applyingit will now be described with reference to the accompanying drawings,but it is to be clear that variations in these methods can be carriedout within the appended claims.

In the drawings FIG. 1 shows a simple method in which a minimum numberof steps are used, step 1 consisting in supporting a charge 1 on aphotoconductor surface 2 on a backing member 3, the photoconductorsurface taking any of the known forms such as a film of vacuum depositedselenium on a base, or a zinc oxide photoconductor embedded in a resinfilm or the like applied to a thin aluminum or paper backing or othersupport, the charge 1 being applied in any manner such as by firstsubjecting the photoconductor surface to a corona discharge and thenlight-bleeding the surface through a negative or the like to leave alatent electrostatic image of the pattern which it is desired toproduce.

Step 2 consists in developing the latent electrostatic image with afirst liquid which may be achieved by passing a roller 4 over thesurface, the roller being pervious and carrying the necessary developingliquid so that a developed image 5 is produced on the photoconductor 2which will be held thereto by the charge.

Step 3 consists in applying the second liquid 6 thereto preferably bymeans of a roller 7 which carries the liquid,

the wetting of the photoconductor by this liquid taking place only inthose areas where the developer 5 was not attracted to and held on thephotoconductor surface, this being because the two liquids must benon-compatible so that the first applied liquid 5 controls thedeposition of the second liquid 6.

The liquid 6 in this case has in it a decomposing agent for thephotoconductor and therefore after it is applied to the surface thephotoconductor will be decomposed, and in step 4 is then shown how bymeans of a jet of Water or other liquid, applied with suflicient force,the second liquid and the decomposed photoconductor are removed.

The jet or brush is designated 8 and the area from which thephotoconductor has been removed is designated 9.

The jet may of course remove both of the liquids, that is the firstliquid 5 and the second liquid 6, but as the first liquid 5 did notcontain a decomposing agent it will be obvious that the photoconductorwhich is protected thereby will remain intact and therefore during thewashing operation, even if both liquids are removed, the one area willhave the photoconductor removed because of the decomposing action whilethe other area will still retain the photoconductor.

In this way of course a master can be readily produced using forinstance an aluminum base or plastic base or film base on which thephotoconductor surface, such as an organic photoconductor surface, washeld, the process permitting the master to be continuously produced inthat the first liquid is simply put down onto the developed image, thesecond liquid containing the decomposing substance is then applied, andafter decomposition has taken place the liquids are removed by washingor abrasion or the like, whereupon a master will result which has areaswhere the aluminum or plastic is exposed and areas where thephotoconductor remains in place, these areas then defining an imagewhich can immediately be used in offset printing or for any otherfurther processing if that is required.

The advantage of the process of course is that there is no dryingbetween the steps and the whole process can be carried out in theshortest possible time.

In the embodiments shown in FIG. 2, step 1 shows the latentelectrostatic image 10 on a photoconductor 11 on a base 12, step 2showing how the roller 13 applies the developer 14 to the latentelectrostatic image 10, step 3 showing the application by means of theroller 15 of the second liquid 16 which in this case can simply be apolar substance, the first developer 14 having been an insulatingliquid, both liquids in this case being retained on the surfaceaccording to the original electrostatic pattern, step 4 showing how bymeans of a roller 17 a decomposing liquid 18 can be applied to thesurface, the decomposing liquid of course in this case being given anaffinity for or solubility in the liquid 16 so that it is absorbed orheld by this liquid and therefore causes the liquid to become adecomposing agent to act on the photoconductor in the area concerned,step 5 showing how by means of the jet 19 the liquid and photoconductorare removed from the area 20 whereas the area 21 will retain thephotoconductor because of the protection afforded by the liquid 14.

It will be obvious that using this further step, and first of all usingtwo selective liquids on the photoconductor surface, the decomposingagent could be made compatible with either the liquid 16 or the liquid14 and therefore instead of it being absorbed by the liquid 16 as shownin FIG. 2 it could be absorbed by the insulating liquid 14 so that theopposite areas of the photoconductor surface would then be removed.

Example 1.The paper, plastic, metal or other sheet which it is desiredto use as a backing is first coated with a photoconductive layer havingthe following composition:

Grams Photoconductive zinc oxide (such as Durham Special supplied byHarrisons Ramsay Ltd.) Resin, long oil alkyl (such as Rhodene M8 alkydresin or Lustrasol 180 resin, Reichold Chemical Corp. 30 Dyes:

Rose Bengal 0.1 Sod. fiuorescein 0.01 Brilliant green 0.01 Driers 0.02Toluene 50 After curing for 6-8 hours at F. the coating is ready for usein the selective process of the present invention. The sheet is chargedelectrostatically at a field strength of 10 kv./inch to produce anoverall surface charge equivalent to approximately 300 v. potential.

The sheet is then exposed to the desired subject and developed in adeveloper prepared as follows:

Shellsol T9O parts by volume (a hydrocarbon liquid by the Shell Company)Silicone fluid-10 parts by volume (such as Dow Corning silicone fluid,viscosity 200 cps.)

These ingredients are blended together to produce a Ml. Shellsol T 60Water 40 Wetting agent, Nonidet P40 (Shell Company) 1 These liquids areshaken vigorously in a shaking vessel to produce an emulsion. Thisemulsion produces selective wetting of the image areas with Shellsol Tand the nonimage areas with water.

The still wet sheet is now immersed in a bath containing a solution ofpotassium hydroxide in ethyl alcohol, for example a solution for aperiod of seconds to decompose the photoconductor in the watercontaining non-image areas where the decomposing liquid is miscible withthe liquid already there, and the sheet is then removed to a water bathor water spray and the coating is washed from the non-image areas. Forprinting purposes the sheet is then wetted with a wetting agent such as5% disodium hydrogen phosphate solution in water or a solution of acommercial plate preparation such as Playtex and subsequently inked forprinting.

On a metal backing the sheet can now be etched selectively and deeplyfor such applications as printing blocks and also for forming smallparts from thin sheet metal.

Example 2.This can be similar to Example 1 but instead of using aninsulating liquid developer (silicone fluid) a concentrated developer isfirst produced having the following composition:

. Grams Monolite Red, I.C.I. Lithographic varnish 200 Pentacite P423 gum100 Cyclohexane 20 The concentrate is mixed in a bar mill to produce apaste. This concentrate is dispersed in Shellsol T or other hydrocarbonsolvent having for example a flash point of F. and containing zeroaromatics, in the proportions 1 gram of paste to 100 grams of ShellsolT.

This developer is then used as in Example 1 but gives a somewhat moresolidly adhering first developer but again having the effect ofshielding the image against action by the second liquid.

Example 3.In Example 1 or 2 an aluminum sheet may be etched afterimaging and removal of the coating to etch form a metal part. Theetchant can be for example hydrofiuoric acid 10%.

Example 4.In Example 1 or 2 the sheet can comprise a glass backingcoated with zinc oxide, bismuth trioxide, lead iodide, cadmium sulphide,cadmium selenide or the like. After removal of the coating from thebacking in the non-image area the glass can be etched selectively withhydrofluoric acid.

Example 5.In Example 1 or 2 a brass sheet can be used and afterselective removal of the coating the sheet can be selectivelyelectroplated with gold, chromium, silver, nickel and the like.

Example 6.-The paper, plastic, metal, wood or other sheet can be coatedin a vacuum chamber with a thin film of amorphous photoinsulativeselenium or sulphur or arsenic trichloride to a thickness of, forexample, 0.5 to 5 microns. The sheet is then charged, exposed anddeveloped with a developer of the type shown in Example 1 or 2 modifiedfor example by the substitution of Microlith Black CT for the MonoliteRed, and Mineral Turpentine (45% aromatics) for the Shellsol T. Thesheet is then selectively wetted in an emulsion having a similarcomposition to that of Example 1 or 2, modified if desired by the use ofTeepol as a surfactant instead of Nonidet.

The plate after selective Wetting can be treated to remove the seleniumfrom the non-image areas by the application of a 10% solution of causticsoda NaOH in water or methyl alcohol. The sheet can then be used forsimilar lithographic or letterpress printing block or transparencypurposes.

Example 7.In Example 6, the selectively dissolved selenium plate canhave a glass backing or film base. After removal of the selenium fromthe non-image areas and selectively from the continuous tones, atransparency having high resolving power results.

Example 8.-In Example 6, the backing can be zinc engraving plate and thefinal step can be deep etching for letterpress printing.

Example 9.In Example 6, the backing can be glass and the developer ofExample 2 can comprise ceramic powders with flux. Following completionthese powders can be fired into the glass by heating in a furnace, forexample to 800 C.

Example 1 0.-T he paper, plastic, metal, wood or other sheet can becoated by dip coating or vacuum evaporation or with an organicphotoconductor, for example an organic photoconductor coated platemarketed by Kalle A. G. Germany. The sheet is then charged, exposed, anddeveloped with a developer of the type shown in Example 2, modified ifdesired by the use of Peerless Carbon Black for the Monolite Red, anddispersed in Shellsol T. The emulsion used in Example 2 for selectivewetting can be modified if desired by the use of white spirits and watertogether with a suitable surfactant such as Teepol, or triethanolamineoleate. In the selective removal of the organic photoconductor coating asolution of 5% potassium hydroxide in water is used for a period of 10seconds to remove the organic photoconductor from the non-image areas.The plate can then be readily used for lithography.

Example 11.In Example 9, the plate can be aluminum and the end productan etch formed part after etching with hydrofluoric acid, 1 to 10% inwater.

Example 12.In Example 1, 2, 6 or 8, the plate can be a printed circuitlaminate and the copper sheet contained thereon can be removed byetching with ferric chloride or acid or the like after selective removalof the photoconductor. Copper conductors can then be formed in thedesired areas which retain continuity and edge sharpness in an improvedmanner.

Example 13.-In Example 1, 2, 6 or 10, the plate can be fabric, cotton,wool, synthetic fibres and the like and the web can be selectively dyedor printed.

It will be seen from these examples that one modi fication of ourprocess consists of exposing and develop ing a surface carrying anoleophilic image whilst still wet, selectively wetting said plate withanother liquid, then selectively dissolving or decomposing the coatingin selected areas to produce a selective resist for subsequent attack orpost treatment of the underlying sheet or plate.

Example 14.In Example 2, in the removal step, there is substituted forthe solution of potassium hydroxide in ethyl alcohol, a solution ofoleic acid in xylene, which selecting softens the image areas which arewater wet. After heating the wetted sheet for 1 minute at F. thesoftened image areas are removed by wiping with xylene, cumene, mineralturpentine or the like.

Example 15.In Example 6, where a thin film of amorphous selenium is thephotoconductor the potassium hydroxide in ethyl alcohol solution isreplaced by a solution of potassium sulphide or sodium sulphide in ahigher alcohol or by carbon disulphide.

Example 16.-In Example 10, where the photoconductor film is an organicphotoconductor the potassium hydroxide solution is replaced by asolution of benzene or high aromatic solvent.

Example 17.-The zinc oxide-resin coated sheet is Grams Water soluble gum(such as starch) Shellsol T, hydrocarbon solvent 50 These compounds areground together to form a paste and then dispersed in Shellsol T in theproportions 1 gram of paste to 100 grams of Shellsol T. This dispersionis used to develop the image, the gum going down on to the chargeretaining area and the hydrocarbon solvent wetting the remaining areas.The sheet is then subjected to water (which forms the second liquid ofthis process) to remove the water soluble gum and go down in its place,the non-image areas which were Wetted with Shellsol T being unaffectedby this washing and these areas will resist subsequent acid attack. Thewater wetted image areas are now subjected to an acid, for example 30%acetic acid which is miscible with the water and decomposes the zincoxide. The sheet can be inked up selectively and subjected to furtherdecomposition Where necessary for example in etching a glass backing.

Example 18. In Example 17, where the photoconductor is zinc oxide,replacing the starch with gum acacia, gum tragacanth, ethyl celluloseand the like.

Example 19.In example 17, where the photoconductor is replaced byselenium, the gum is replaced by potassium sulphide, this is ground upinto a fine powder and dispersed in a similar manner to the gum. Uponwetting with water, the potassium sulphide attacks the selenium andenables its removal.

Example 20.In Example 17, the photoconductor is replaced by an organicphotoconductor such as poly (npropenylcarbazole) and the gum is replacedby an organic acid such as palmetic acid, lauric acid, myristic acid andthe like dispersed in a high boiling point hydrocarbon solvent or in asilicone oil or paraffin oil or the like.

Example 21 .-In any of the foregoing examples, the etch solution or thelike is replaced by a solution of a ketone such as acetone in water forExample 1 to 10% acetone.

Example 22.In the foregoing example, the ethyl alcohol or the like isreplaced by a solution of an aldehyde in alcohol or water for example a1% solution.

Example 23.In the foregoing examples where the coating is resin-bound oris an organic photoconductor the etch solution or the coating isreplaced by a solution of chlorothene in alcohol.

What we claim is:

1. A method of conditioning a photoconductor surface comprising thesteps of producing an electrostatic latent image on a photoconductorsurface on a base, developing the electrostatic latent image by applyingto the surface Cir a first developer liquid at least part of which isattractable to the charged areas of the latent electrostatic image, ap-

plying to the surface a second liquid which is immiscible with the firstliquid, at decomposing agent for the photoconductor surface which ismiscible with only one of the said liquids being incorporated into saidone liquid for selective decomposition of part of said surface, and thenremoving the photoconductor surface where decomposed.

2. The method according to claim 1 wherein the first liquid is anelectrical insulator and the second liquid is a polar liquid.

3. The method according to claim 1 wherein the first developer liquidcomprises an electrically insulating carrier liquid, and carried thereinparticles which are attractable to the image area and which retain theliquid at the image area.

4. The method according to claim 1 wherein the first developer liquidcomprises an electrically insulating liquid and carries thereinparticles which are attractable to the image area and which retain theliquid at the image area only while the particles remain, said liquidwetting the non-image areas, then with the liquid of the first de-.veloper liquid on the non-image areas wetting the image area with saidsecond liquid. i

5. The method according to claim 1 comprising the further step ofetching the base where thephotoconductor is removed.

6. The method according to claim 1 comprising the further step ofapplying a coating to the base where the photoconductor is removed.

7. The method according to claim 1 wherein the decomposing agent isincorporated into said one liquid before the latter is applied to saidsurface.

8. The method according to claim 1 wherein the de composing agent isincorporated into said one liquid after the latter is applied to saidsurface.

9. The method according to claim 1 wherein the decomposing agent isselected from the group consisting of potassium hydroxide, sodiumsulphide and sodium hydroxide in solution.

10. The method according to claim 9 wherein the surface is selected fromthe group consisting of zinc oxide and selenium.

References Cited UNITED STATES PATENTS 2,732,228 1/ 1956 Propstl 156-'32,857,271 10/1958 Sugarman 96-1 3,104,169 9/1963 Metcalfe et al. 9613,257,204- 6/1966 Sus et al. 96--1.5 3,291,738 12/ 1966 Sciambi 252-62.13,305,359 2/1967 Delrnont 96-4 3,311,490 3/1967 Fauser et al. 11737NORMAN G. TORCHIN,-Primary Examiner.

C. E. VANHORN, Assistant Examiner.

